The present invention relates to the field of audio/visual content. More specifically, one embodiment of the invention provides a system for synchronizing command execution.
The amount of multimedia content available on the World Wide Web and in numerous other databases is growing out of control. However, the enthusiasm for developing multimedia content has led to increasing difficulties in managing, accessing, and identifying the content mostly due to their volume. To address this problem, MPEG-7 is being developed by the Moving Pictures Expert Group (MPEG), which is a working group of ISO/IEC. In contrast to preceding MPEG standards such as MPEG-1 and MPEG-2, which relate to coded representation of audio-visual content, MPEG-7 is directed to representing information relating to content, and not the content itself.
The MPEG-7 standard, formally called the “Multimedia Content Description Interface” seeks to provide a rich set of standardized tools for describing multimedia content. The objective is to provide a single standard for providing interoperable, simple, and flexible solutions to the aforementioned problems vis-à-vis indexing, searching, and retrieving multimedia content. It is anticipated that software and hardware systems for efficiently generating and interpreting MPEG-7 descriptions will be developed.
More specifically, MPEG-7 defines and standardizes the following: (1) a core set of Descriptors (Ds)for describing the various features of multimedia content; (2) Description Schemes (DSs) which are pre-defined structures of Descriptors and their relationships; and (3) a Description Definition Language (DDL) for defining Description Schemes and Descriptors.
A Descriptor (D) defines both the semantics and the syntax for representing a particular feature of audiovisual content. A feature is a distinctive characteristic of the data which is of significance to a user.
As noted, DSs are pre-defined structures of Descriptors and their relationships. Specifically, the DS sets forth the structure and semantics of the relationships between its components having either Descriptors and/or Description Schemes. To describe audiovisual content, a concept known as syntactic structure which specifies the physical and logical structure of audiovisual content is utilized.
The Description Definition Language (DDL) is the language that allows the creation of new Description Schemes and Descriptors. It also allows the extension and modification of existing Description Schemes. The DDL has to be able to express spatial, temporal, structural, and conceptual relationships between the elements of a DS, and between DSs.
In an MPEG-7 environment, a client describes content in terms of XML/DDL-based MPEG-7 instant documents. In general, these instant documents are represented by a tree where nodes represent different Ds and DSs. Two elements created by DDL, called “Command DS” and “CommandScript” with their associated syntax (schema), allow the dynamic update of these DDL-based MPEG-7 instant documents. CommandDS allows a server, for example, to dynamically update the structure of client instant document by issuing update commands such as “add”, “delete”, and “change”.
More specifically, CommandDS provides a means to perform a set of operations on the nodes of a content description tree. The operations include adding a node before or after a specified node, changing the node to a new node, changing the node's value, and deleting the node.